17:15 〜 19:15
[HTT16-P09] MC-ICP-MSを用いたストロンチウム同位体比測定に及ぼすコーンの組み合わせの影響
キーワード：ストロンチウム同位体、MC-ICP-MS、ジェットインターフェース、質量差別効果
1. Introduction
In isotope ratio measurements using Neptune Plus (Thermo Fisher Scientific Inc.) MC-ICP-MS system, the combination of a Jet sample cone and an X skimmer cone (hereinafter called "Jet/X") is available for the measurement of low-concentration samples because it improves detection sensitivity compared to that when using a standard sample cone and a H skimmer cone combination (hereinafter called "Standard/H"). On the other hand, there are several reports that the use of Jet/X led to the instrumental mass discrimination that cannot be corrected by the exponential law for some target elements (K. Newman (2012) JAAS, 27, 63-70) and the enhancement of oxide formations that causes polyatomic ion interferences (S. Louwens et al. (2017) JAAS, 32, 597-608). Therefore, the applicability of Jet/X to isotope ratio measurements needs to be carefully evaluated for each target element. Although there are several cases in which Jet/X has been applied to Sr isotope ratio measurements (e.g., J. DeBord et al. (2017) Inorg. Chim. Acta, 468, 294-299), the reliability of the method using Jet/X has not been adequately evaluated. In this study, to evaluate the applicability of Jet/X to 87Sr/86Sr and 88Sr/86Sr measurements, the following aspects were compared with those of Standard/H: (1) accuracy, precision, and sensitivity of the measurements, (2) extent of the instrumental mass discrimination, and (3) behavior of spectroscopic interference from a concomitant element (i.e., Ca, which possibly causes polyatomic interferences at Sr isotope ratio measurements). In addition, the applicability of Jet/X for matrix-type samples was evaluated by measuring the 87Sr/86Sr ratios and the δ88/86Sr values of JCp-1 coral reference material and FEBS-1 otolith reference material, which have been well studied in the literature.
2. Experimental
Instrumentation: A Neptune Plus MC-ICP-MS was used for the measurements at dry plasma condition. To compare Jet/X with Standard/H, all samples were analyzed using Jet/X and Standard/H, respectively.
Data processing: For the elimination of instrumental mass discrimination, an internal correction technique based on the exponential law using 88Sr/86Sr as a reference isotopic ratio was employed in 87Sr/86Sr measurements, and an empirical external normalization approach using 92Zr/90Zr as an external standard combined with the standard-sample bracketing method was used in 88Sr/86Sr measurements.
Reagents and materials: The Sr isotopic standard, NIST SRM 987 was repeated analyzed. To evaluate the behavior of spectroscopic interference from Ca, the NIST SRM 987 spiked with various amounts of Ca standard solution (Kanto Chemical Co., Inc.) were analyzed. The Sr/matrix separations of JCp-1 (Geological Survey of Japan) and FEBS-1 (National Research Council of Canada) were carried out using Sr resinTM (Eichrom Technologies Inc).
3. Results
The measured 87Sr/86Sr ratios and δ88/86Sr values of NIST SRM 987 using Jet/X were in good agreement with those using Standard/H and literature values. The signal intensity of 88Sr was improved by a factor of 4 when using Jet/X compared to that when using Standard/H, resulting in precise measurements of lower Sr concentrations (i.e., 50 μg kg-1) with comparable precision to that of measurements of 200 μg kg-1 Sr using Standard/H. No significant difference in the magnitude of Ca-induced spectral interference was observed between Jet/X and Standard/H at Ca/Sr concentration ratios of ≦10, suggesting that Jet/X can be used for matrix-type samples if the Sr/matrix separation procedure is properly conducted. The measured 87Sr/86Sr ratios and δ88/86Sr values of JCp-1 and FEBS-1 were in good agreement with those using Standard/H and literature values. These results indicate that Jet/X can be used for reliable measurement of Sr isotope ratios of matrix-type samples, even at Sr concentrations as low as 50 μg kg-1.
In isotope ratio measurements using Neptune Plus (Thermo Fisher Scientific Inc.) MC-ICP-MS system, the combination of a Jet sample cone and an X skimmer cone (hereinafter called "Jet/X") is available for the measurement of low-concentration samples because it improves detection sensitivity compared to that when using a standard sample cone and a H skimmer cone combination (hereinafter called "Standard/H"). On the other hand, there are several reports that the use of Jet/X led to the instrumental mass discrimination that cannot be corrected by the exponential law for some target elements (K. Newman (2012) JAAS, 27, 63-70) and the enhancement of oxide formations that causes polyatomic ion interferences (S. Louwens et al. (2017) JAAS, 32, 597-608). Therefore, the applicability of Jet/X to isotope ratio measurements needs to be carefully evaluated for each target element. Although there are several cases in which Jet/X has been applied to Sr isotope ratio measurements (e.g., J. DeBord et al. (2017) Inorg. Chim. Acta, 468, 294-299), the reliability of the method using Jet/X has not been adequately evaluated. In this study, to evaluate the applicability of Jet/X to 87Sr/86Sr and 88Sr/86Sr measurements, the following aspects were compared with those of Standard/H: (1) accuracy, precision, and sensitivity of the measurements, (2) extent of the instrumental mass discrimination, and (3) behavior of spectroscopic interference from a concomitant element (i.e., Ca, which possibly causes polyatomic interferences at Sr isotope ratio measurements). In addition, the applicability of Jet/X for matrix-type samples was evaluated by measuring the 87Sr/86Sr ratios and the δ88/86Sr values of JCp-1 coral reference material and FEBS-1 otolith reference material, which have been well studied in the literature.
2. Experimental
Instrumentation: A Neptune Plus MC-ICP-MS was used for the measurements at dry plasma condition. To compare Jet/X with Standard/H, all samples were analyzed using Jet/X and Standard/H, respectively.
Data processing: For the elimination of instrumental mass discrimination, an internal correction technique based on the exponential law using 88Sr/86Sr as a reference isotopic ratio was employed in 87Sr/86Sr measurements, and an empirical external normalization approach using 92Zr/90Zr as an external standard combined with the standard-sample bracketing method was used in 88Sr/86Sr measurements.
Reagents and materials: The Sr isotopic standard, NIST SRM 987 was repeated analyzed. To evaluate the behavior of spectroscopic interference from Ca, the NIST SRM 987 spiked with various amounts of Ca standard solution (Kanto Chemical Co., Inc.) were analyzed. The Sr/matrix separations of JCp-1 (Geological Survey of Japan) and FEBS-1 (National Research Council of Canada) were carried out using Sr resinTM (Eichrom Technologies Inc).
3. Results
The measured 87Sr/86Sr ratios and δ88/86Sr values of NIST SRM 987 using Jet/X were in good agreement with those using Standard/H and literature values. The signal intensity of 88Sr was improved by a factor of 4 when using Jet/X compared to that when using Standard/H, resulting in precise measurements of lower Sr concentrations (i.e., 50 μg kg-1) with comparable precision to that of measurements of 200 μg kg-1 Sr using Standard/H. No significant difference in the magnitude of Ca-induced spectral interference was observed between Jet/X and Standard/H at Ca/Sr concentration ratios of ≦10, suggesting that Jet/X can be used for matrix-type samples if the Sr/matrix separation procedure is properly conducted. The measured 87Sr/86Sr ratios and δ88/86Sr values of JCp-1 and FEBS-1 were in good agreement with those using Standard/H and literature values. These results indicate that Jet/X can be used for reliable measurement of Sr isotope ratios of matrix-type samples, even at Sr concentrations as low as 50 μg kg-1.